diff --git a/lib/OpenLayers/Popup.js b/lib/OpenLayers/Popup.js
index 7810026966..c4ae7bfd1a 100644
--- a/lib/OpenLayers/Popup.js
+++ b/lib/OpenLayers/Popup.js
@@ -109,7 +109,7 @@ OpenLayers.Popup.prototype = {
      */
     updatePosition: function() {
         if ((this.lonlat) && (this.map)) {
-                px = this.map.getLayerPxFromLonLat(this.lonlat);
+                var px = this.map.getLayerPxFromLonLat(this.lonlat);
                 this.moveTo(px);            
         }
     },